Erodible soil bulkhead

ABSTRACT

The Erodible Soil Bulkhead (ESB) is a coastal beach protection system that protects existing coastal bluffs and shorelines from wave erosion while at the same time providing controlled time release of soil to the beach to help sustain natural habitat for marine life. The ESB is intended to provide protection to coastal shoreline areas where conventional “hard” beach protection (e.g., rock, concrete or steel structures) is not preferred or allowed by regulatory agencies due to detrimental effects on the coastal marine environment. The ESB is constructed with natural soils which are strengthened via degradable reinforcing an/or cementing agents to have a greater erosion resistance than untreated fill soil while remaining, to a controlled degree, erodible. By its nature the ESB is disposable and must be re-constructed at the end of its useful life to continue providing protection to the shoreline and/or structures.  
     The ESB is constructed on the beach, normally seaward of the existing eroded shoreline. The ESB is constructed with natural soils which are strengthened via reinforcing an/or cementation to have a greater erosion resistance than conventional fill soil while remaining, to a controlled degree, erodible. Erosion resistance is provided by biodegradable reinforcing and/or by mixing the soil with portland cement or other agent to provide cementation. The degree of erosion resistance is controlled by the nature and amount of reinforcing provided and/or by the amount of cementing agent and admixtures mixed with the soils. Untreated soils may be placed on top of the treated erosion resistant soils to provide additional volume of erodible soils to the beach as controlled recession of the ESB occurs.  
     The ESB extends as far as practical seaward of the existing shoreline (as limited by physical beach conditions and/or regulatory agencies). Typically the width of the ESB will be about 10 to 30 feet but could be larger. Height of the erosion resistant portion of the ESB will depend on the local tidal range, wave action and site specific geotechnical conditions but generally ranges from about 6 to 8 feet above the beach level. Additional height of untreated soils above the erosion resistant lower portion can range from none to maximum heights limited only by site geometry and stability of the overall ESB.  
     Where reinforcing is used to provide erosion resistance, the reinforcing is normally commercially manufactured, ultraviolet-degradable geotextile products. The geotextile is placed within compacted granular soil fill to form a reinforced soil mass by layering geotextile and soil or by forming geotextile wrapped soil tubes. The seaward side of the geotextile ESB is initially closed by wrapping the geotextile back into the reinforced soil. As degradation of the geotextile occurs due to daily exposure to natural elements (including ultraviolet light), the soil of the ESB is exposed to wave action and erosion occurs. As soil erosion occurs, the geotextile reinforcing is undermined and the newly exposed fabric droops down, covering the seaward face of the ESB which reduces the erosion rate of the soils. The process is repeated as the newly exposed geotextile degrades and additional soil erosion occurs.  
     Where cementation is used to provide erosion resistance, the cementing agent is mixed with the soil to provide sufficient unconfined compressive strength to control erosion to the desired rate. The amount of cemention required to control erosion varies from site to site and possibly from point to point within the ESB at a particular site. Typically the ratio of portland cement to soil will range from about 1% to 10% by weight depending on site conditions. The soil-cement mixture can be mixed and placed on-site, provided conditions will allow, or the soil-cement can be mixed off-site and delivered to the site for placement.

BACKGROUND OF THE INVENTION

[0001] The Erodible Soil Bulkhead (ESB) is applicable to the fields ofgeotechnical engineering, general construction as well as marineengineering and construction pertaining to coastal erosion. Wave erosionoccurs on an ongoing basis at most unprotected shorelines and in manycases the stability of near-beach development becomes threatened overtime by undermining due to progressive beach erosion. In the pastconventional “hard” beach protection (e.g., rock, concrete or steelstructures) have been used to provide protection from further waveerosion, however “hard” protection is no longer acceptable to somelocal, state and federal regulatory agencies because they havedetermined that the soil added to the near-shore environment fromongoing beach erosion is essential to sustaining natural habitat formarine life (and in particular some endangered species) and “hard”structures stop the natural flow of eroded soil to the beach. The ESB isintended to solve the existing problem of protecting coastal shorelinesand development from the effects of wave erosion while at the same timeproviding controlled erosion of soil to the beach to help sustain thenatural marine habitat.

[0002] Existing information which is utilized in this invention includethe procedures for design, mixing and placing soil-cement mixtures (seePortland Cement Association documents pertaining to soil-cement) and themanufactures brochures and technical specifications for the numerousgeotextiles currently available through local and regional salesrepresentatives.

BRIEF SUMMARY OF THE INVENTION

[0003] The Erodible Soil Bulkhead (ESB) is a coastal beach protectionsystem that protects existing coastal bluffs and shorelines from waveerosion for a period of time while at the same time providing controlledtime release of soil to the beach to help sustain natural habitat formarine life. The ESB is intended to provide protection to coastalbeach/bluff areas where conventional “hard” beach protection (e.g.,rock, concrete or steel structures) is not preferred or allowed byregulatory agencies due to detrimental effects on the coastal marineenvironment.

[0004] The ESB solves the existing problem of protecting existingcoastal shorelines and development from the effects of wave erosionwhile at the same time providing controlled release of soil to the beachto help sustain the natural marine habitat. The ESB is constructed withnatural soils which are strengthened via reinforcing an/or cementationto have a greater erosion resistance than conventional fill soil whileremaining, to a controlled degree, erodible. Erosion resistance isprovided by degradable reinforcing and/or by mixing the soil with acementing agent to provide additional strength. The degree of erosionresistance is controlled by the nature and amount of reinforcingprovided and/or by the amount of cementing agent mixed with the soils.Untreated soils are placed on top of the treated erosion resistant soilsto provide additional volume of erodible soils to the beach ascontrolled recession of the treated soils of the ESB occurs.

BRIEF DESCRIPTION OF FIGURES

[0005]FIG. 1:

[0006] Presents a side view, partial top view and partial end view of athe general concept of the Erodible Soil Bulkhead.

[0007]FIG. 2:

[0008] Presents a side view, partial top view and partial end view of aErodible Soil Bulkhead constructed using layered geotextile reinforcing.

[0009]FIG. 3:

[0010] Presents a side view, partial top view and partial end view of aErodible Soil Bulkhead constructed using soil tube geotextilereinforcing.

[0011]FIG. 4:

[0012] Presents a side view, partial top view and partial end view of aErodible Soil Bulkhead constructed using soil-cement mixture.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The Erodible Soil Bulkhead (ESB) is a coastal beach protectionsystem that provides wave erosion protection to existing coastal bluffsand shorelines from wave erosion while at the same time providingcontrolled release of soil to the beach to help sustain natural habitatfor marine life (see FIG. 1). The ESB is intended to provide protectionto coastal beach/bluff areas where conventional “hard” beach protection(e.g., rock, concrete or steel structures) is not preferred or allowedby regulatory agencies due to detrimental effects on the coastal marineenvironment. By its nature the ESB is disposable and must bere-constructed at the end of its useful life to continue providingprotection to the developed shoreline and/or structures.

[0014] The ESB is constructed on the beach, normally seaward of theexisting eroded shoreline. The ESB extends as far as practical seawardof the existing shoreline (as limited by physical beach conditionsand/or regulatory agencies). Typically the width of the ESB will beabout 10 to 30 feet but could be larger. Height of the erosion resistantportion of the ESB will depend on the local tidal range, wave action andsite specific geotechnical conditions but generally ranges from about 6to 8 feet above the beach level. Additional height of untreated soilsabove the erosion resistant lower portion is limited only by sitegeometry and stability of the overall ESB.

[0015] The ESB is constructed with natural soils which are strengthenedvia reinforcing an/or cementation to have much greater erosionresistance than conventional fill soil while remaining, to a controlleddegree, erodible. Erosion resistance is provided byenvironmentally-degradable reinforcing (reinforcing which degrades whenexposed to natural sunlight and/or natural organisms) and/or by mixingthe soil with a cementing agent such as portland cement to providecementation. The degree of erosion resistance is controlled by theamount and degredation characteristics of the reinforcing materialand/or by the amount of cementing agent mixed with the soils. Untreatedsoils are placed on top of the treated erosion resistant soils toprovide additional volume of erodible soils to the beach as controlledrecession of the treated soils occurs.

[0016] Where reinforcing is used to provide erosion resistance, theprimary reinforcing is normally commercially availableultraviolet-degradable geotextile products (see FIGS. 2 and 3) althoughother types of degradable reinforcing can be used. Geotextiles havepreviously been used as soil reinforcing in the design and constructionof reinforced soil retaining structures and slopes, as well as filtersfor subsurface water flow and surface stabilization to prevent erosion.The unique difference of the use of geotextiles in the ESB is that to myknowledge geotextiles have never been used to allow erosion to occur ata controlled rate as they are in the ESB. In addition to my knowledgethe geotextile wrapped soil tubes configuration of the ESB reinforcementhas not been previously used.

[0017] Where cementation is used to provide erosion resistance (see FIG.4), a cementing agent such as portland cement is mixed with the soil toprovide sufficient unconfined compressive strength to control erosion tothe desired rate. The concept of mixing a cementing agent with soil toincrease soil strength has been used for many years. The uniquedifference of the use of cemented soil in the ESB is that the cementedsoil mixture is intended to allow erosion of the soil at a controlledrate.

[0018] ESB Construction Using Geotextile

[0019] Geotextile is placed within compacted granular soil fill to forma reinforced soil mass by layering geotextile and soil (see FIG. 2) orby forming geotextile wrapped soil tubes (see FIG. 3). The seaward sideof the geotextile ESB is initially closed by wrapping the geotextileback into the reinforced soil. As degradation of the geotextile occursdue to daily exposure to natural elements (including ultraviolet light),the soil of the ESB is exposed to wave action and erosion occurs. Assoil erosion occurs, the geotextile reinforcing is undermined and thenewly exposed fabric droops down, covering the seaward face of the ESBwhich reduces the erosion rate of the soils. The process is repeated asthe newly exposed geotextile degrades, and additional soil erosionoccurs.

[0020] ESB construction using layered geotextile reinforcing (see FIG.2) is similar to that of a conventional reinforced soil structure exceptthat the geotextile layers may be more closely spaced than normalreinforced soil structures. A geotextile layer is placed on a preparedsoil surface and a layer of soil is placed over it and compacted to aspecified density. Construction proceeds to the design height of the ESBby placing a new layer of geotextile over the previously compacted soillayer and subsequently placing and compacting another layer of soil.

[0021] ESB construction using soil filled geotextile tubes (see FIG. 3)is accomplished by using a form which is lined with geotextile and thenfilled with soil. The top seam of the tubes are fastened usingbiodegradable pins and/or twine. Tubes constructed using the form areconstructed about one tube diameter apart and the intermediate tubes areconstructed to fill the space between the formed tubes. The tubes areoriented with the long dimension approximately perpendicular to thebeach line in general as shown in FIG. 2, but can be oriented atdifferent angles as required for existing site conditions and endprotection. Each layer of tubes are laid side-by-side across the lengthof the beach to be protected. Subsequent layers of the soil tubes areformed in the same manner and are stacked vertically to the designheight of the ESB. Diameter of the tubes and the ultra-violetdegradation rate of the geo-textile is varied to control the rate oferosion. Supplemental biological reinforcement can be provided byplanting trees, shrubs, etc. on the ESB.

[0022] ESB Construction Using Portland Cement-Soil Mixture

[0023] A typical soil-cement ESB is shown on FIG. 4. The soil-cementmixture can be mixed and placed on-site, provided conditions will allow,or the soil-cement can be mixed off-site and delivered to the site forplacement. The amount of portland cement required to control erosionwill vary from site to site and possibly from point to point within theESB at a particular site. Typically the cement to soil ratio will rangefrom about 1% to 10% by weight depending on site conditions.

[0024] On-Site Mixed Soil-Cement

[0025] A temporary form such as stackable concrete blocks (commonlycalled “ecology blocks” in the Puget Sound Region) or other suitablesystem is placed along the seaward limit of the ESB. Natural soilmaterial is placed behind the form in controlled thickness layers,cement is spread on the surface at the proper ratio, water is added asnecessary and the soil and cement are mixed with a traveling mixingmachine. Alternatively a on-site batch mixer could be used and the mixedsoil-cement batch material would be transported and placed in layers.The mixed soil-cement layer is then compacted to a specified dry densityusing conventional soil compaction equipment. The process is repeated toconstruct the ESB and the temporary forms are removed to allow theerosion process to begin.

[0026] Off-Site Mixed Soil-Cement

[0027] Limited size temporary forms are used to support the off-sitemixed soil cement when it is delivered to the site. The size and shapeof the forms volume will vary depending upon the ESB design, logisticalconstraints of soil-cement delivery to the site and the time constraintsof tidal water level fluctuations at the site. The soil-cement mixtureis placed into the temporary form and densified as required to achievedesign density. After the soil-cement mixture has gained sufficientstrength, the form is removed. The process is repeated incrementally tocreate the seaward face of the ESB. After completion of the initialseaward face of the ESB, placement of the remaining soil-cement materialbetween the seaward face and the existing shoreline is performed with orwithout forming depending upon the site specific design.

1. I claim as my invention the concept of an Erodible Soil Bulkhead(ESB) system that can provide significant erosion protection ofshoreline (greater protection than a untreated fill soil mass) while atthe same time eroding at a controlled rate to provide an ongoing flow ofsoil to the near-shore marine environment.
 2. I claim as my inventionthe use of geotextile to allow a controlled rate of erosion of a soilmass.
 3. I claim as my invention the use of cementing agents such asportland cement to provide a controlled rate of erosion of a soil mass.